These cards... as arena player can't wait to see them a lot <3 I mean all of them are good (well... except of Firelands Portal which will be like Murloc Knight of TGT and Keeper of Uldaman of LoE. I can see it already, everywhere mages with that card... I'm more having fun on arena rather than picking always mages, paladins and rogues so this would hurt a lil... other cards that than portal for me are masterful and I CAN'T WAIT seeing them in arena <3

Yeah i agree the old website format was better....I think the best solution is hybridizing new and old formats together having the main feature/newest addition being visible on the main page like before...The rest covert into the downsized click version.

Battlecry---->Deaths----->Deathrattle----->Summon. Sylvanas steals deathwing when summoned, but if you summon deathwing against a mad scientist and he gets a mirror entity to the field, you will get a deathwing. Not sure where the deathrattle fits in there.

The reason it works with Deathwing is because minions hit by a Destroy effect are not immediately killed - they are set pending destroy/TO_BE_DESTROYED and killed the next time Hearthstone checks for death, which will be after the Battlecry Phase fully resolves.

Testing it will tell, Hearthstone mechanics can be really weird and it can be up to how the individual cards were programmed. I think Illidan has a similar enough mechanic that testing whether or not he was to summon there might yield the same result.

Some examples for behavious that one would not really expect until they see it:

Mad Scientists secrets can trigger on minions that kill him through battlecries (while at the same time I think that I saw Knife Juggler juggle after getting killed through a Battlecry that caused you to get a minion as well. I'll try it out with a Coldlight Seer some time)

Another weird interaction would be Commanding Shout + Acolyte of Pain. The Commanding Shout still shows you that the minions took damage at 1 Health but they actually mechanically don't, leaving the acolyte to not draw after taking damage at 1 Health.

The reason it works with Deathwing is because minions hit by a Destroy effect are not immediately killed - they are set pending destroy/TO_BE_DESTROYED and killed the next time Hearthstone checks for death, which will be after the Battlecry Phase fully resolves.